Heretofore, research has been conducted on various materials, such as platinum metals and like precious metals supported on activated carbon or carbon black; mixtures of activated carbon and a metal oxide; mixtures of a phthalocyanine metal and carbon powder; and heat-treated products thereof, seeking that are materials usable as a catalyst for the electrode of a fuel cell or an air cell.
Among the above catalytic materials, the platinum supported on activated carbon or carbon black can be obtained by, for example, adding and suspending baked carbon black into hexachloroplatinum acid or a like aqueous solution, subjecting the resulting suspension to evaporation drying and washing with water, and then depositing platinum particles on the surface of the carbon black.
Patent Document 1 discloses that a porous carbon membrane platinum-support structure can be obtained by subjecting a porous polyimide membrane to a heat treatment, forming a hydroxyl group, a carboxyl group or a like functional group in the resulting porous carbon membrane structure, dipping the resulting structure in an aqueous tetraammineplatinum (II) chloride solution to adhere a platinum precursor, and then reducing the thus-obtained platinum precursor.
Patent Documents 2 to 4 disclose a method for producing a metal-containing carbon material, wherein a metal component is dispersed in a polymer, followed by a heat treatment. For example, Patent Document 3 discloses that a carbon onion structure layered around a metal particle is obtained by subjecting a nongraphitizing carbon precursor formed from a resin and a metal nitrate, etc., to a heat treatment. Furthermore, Patent Document 3 also discloses that by additionally supporting precious metal particles (platinum, etc.), the catalytic activity of platinum or the like can be enhanced by the synergistic effect.
The above mentioned platinum metals have a high catalytic activity, but because they are rare and expensive, a manganese oxide is actually used in zinc air cells, etc., as an inexpensive alternative. For example, Patent Document 5 discloses that a catalyst sheet for an oxygen-reduction electrode can be obtained by mixing MnOx having an average particle diameter of not more than 100 nm with activated carbon, carbon black or the like.
[Patent Document 1] Japanese Unexamined Patent Publication No. 2003-128409
[Patent Document 2] Japanese Unexamined Patent Publication No. 1990-109217
[Patent Document 3] Japanese Unexamined Patent Publication No. 2005-19332
[Patent Document 4] Japanese Unexamined Patent Publication No. 2003-53167
[Patent Document 5] Japanese Unexamined Patent Publication No. 2002-93425